This invention relates to silylation of an active-hydrogen-containing compound. In one aspect this invention relates to new methylsilacyclopentenyl-containing compounds which possess unexpected silylating power.
Silylation of active-hydrogen-containing organic compounds for the purposes of chromatographic analysis, organic synthesis and blocking and/or protecting reactive sites in the organic molecule is a well-known and useful procedure. A large number of trimethylsilyl-containing silylating agents and silylating procedures are reviewed by Alan E. Pierce, "Silylation of Organic Compounds," Pierce Chemical Company, Rockford, Ill. (1968).
Silylating agents which provides the trimethylsilyl group are usually used for such purposes because of their commercial availability and because of the desired properties of the resulting trimethylsilylated organic compound, such as higher volatility compared to the unsilylated compound. However, other factors, such as silylating power, and the nature of silylation by-products often are also important in the selection of a silylating agent.
Of the known silylating agents, bis-trimenthylsilylacetamide (hereinafter BSA), provides both availability and high silylating power. However, BSA contains two trimethylsilyl groups, the first of which is responsible for BSA's silylating power. The second trimethylsilyl group in BSA, which remains after the first trimethylsilyl group is reacted is less reactive than the first trimethylsilyl group. Consequently, it is commmon to use one mol of BSA for each active hydrogen atom to be silylated in a silylation reaction and the by-product, trimethylsilylacetamide, is not used in the reaction. Thus, only one-half of the available trimethylsilyl groups are used. A more efficient silylating agent having high silylating power is desired.
We have discovered that silylating agents bearing a methylsilacyclopentenyl group which is bonded to an amido radical or a lactamo radical are powerful and efficient silylating agents.
Methylsilacyclopentenyl-containing compounds bearing a silicon-bonded halogen atom or a silicon-bonded alkoxy radical are diclosed by Atwell in U.S. Pat. No. 3,509,191 which is hereby incorporated by reference to show the preparation of methylsilacyclopentenyl chloride which is a precursor for the preparation of methylsilacyclopentenyl amides and lactams.
Hahn, in U.S. Application No. 644,379, titled "Silacyclopentenyl-bis-epsilon-caprolactam," filed on Dec. 29, 1975 and assigned to the assignee of this invention discloses the title compound and its use as a chain extender for hydroxyl compounds, and especially hydroxyl-endblocked polydimethylsiloxanes, for which it is a very fast chain extender. However, chain extension is a polymerizing process which greatly increases molecular weight and decreases volatility of the polydimethylsiloxane. Such a result is not suitable in a silylating process.
Toporcer, et al., U.S. Pat. No. 3,776,933 discloses a method of preparing amidosilanes of the formula R.sub.x "Si{N(R)C(.dbd.O)R'}.sub.4 -x wherein R" is a monovalent hydrocarbon radical having 1 to 18 carbon atoms and x=1 to 3. Toporcer, et al., state that said amidosilanes are useful as crosslinking agents in silicone rubber, as hydrolyzable silanes to make silicone resins, as chain extenders in silicone rubbers, as endblockers in silicone fluids, as silylating agents and the like. However, Toporcer, et al., do not suggest that methylsilacyclopentenyl amides could be made or that they would be superior silylating agents. U.S. Pat. No. 3,776,933 is hereby incorporated by reference to show a suitable method for preparing the silicon-amide bond.
Silicon-bonded lactams are known from Hurwitz and de Benneville in U.S. Pat. No. 2,876,209 and U.S. Pat. No. 2,876,234. Hurwitz and de Benneville describe silanes containing the lactam group where the generic formula is ##STR2## in which R.degree. is a cyclohexyl group, an aryl group, an alkenyl group or an alkyl group having 1 to 18 carbon atoms, Y is an alkylene group having 3 to 18 carbon atoms with a chain of at least 3 but no more than 5 carbon atoms extending between the N atom and carbonyl group, and x is an integer having a value of 1 to 4. U.S. Pat. No. 2,876,234 is hereby incorporated by reference to show the preparation of the lactam silicon bond.